Diesel engine control device

Abstract

In a diesel engine control device, a normal injection mode that implements normal combustion and a premixed injection mode that implements premixed combustion are set, the normal injection mode is implemented when the actual engine operating conditions are in the normal region, and the premixed injection mode is implemented when the actual engine operating conditions are in the premixed region. When one control mode is being implemented in the corresponding engine operating region, the control mode is forcibly switched to the other control mode when the engine enters a predetermined transition state. This makes it possible to switch earlier than normal, and in particular when accelerating, the desired acceleration performance can be obtained.

1. A diesel engine control device that controls the injection quantity and injection timing of fuel injected into a cylinder of a diesel engine,
 wherein are provided two control modes of: a normal injection mode in which the injection quantity and injection timing are controlled so that the injected fuel ignites near compression top dead center during an injection period; and a premixed injection mode in which the injection quantity and injection timing are controlled so that fuel injection is completed before compression top dead center and the injected fuel ignites near compression top dead center after a premixing period, 
 an entire engine operating region is divided into at least two regions, which are a normal region and a premixed region, 
 the diesel engine control device comprising: normal switching means for switching the control mode so that target values of respective control parameters of the normal injection mode and the premixed injection mode are set in advance separately, the normal injection mode for controlling the control parameters based on the target value set for said normal injection mode is implemented when the actual engine operating conditions are in the normal region, and the premixed injection mode for controlling the control parameters based on the target value set for said premixed injection mode is implemented when the actual engine operating conditions are in the premixed region; and 
 forcible switching means for setting the target values of the control parameters for the normal injection mode in advance in the premixed region and also for setting the target values of the control parameters for the premixed injection mode in advance in the normal region, said forcible switching means for forcibly switching the control mode to the normal injection mode for controlling the control parameters based on the target value for the normal injection mode set in advance in said premixed region when the engine enters a predetermined transition state while, in said premixed region, said premixed injection mode is being implemented and also for forcibly switching the control mode to the premixed injection mode for controlling the control parameters based on the target value for the premixed injection mode set in advance in said normal region when the engine enters the predetermined transition state while, in said normal region, said normal injection mode is being implemented. 
 
   
   
     2. The diesel engine control device according to  claim 1 , wherein when the premixed injection mode is being implemented in the premixed region, and when the engine enters a predetermined acceleration state, the forcible switching means forcibly switches the control mode to the normal injection mode. 
   
   
     3. The diesel engine control device according to  claim 1 , wherein the forcible switching means switches the control mode based on a comparison of a rate of change of an engine load with a predetermined threshold value. 
   
   
     4. The diesel engine control device according to  claim 3 , further comprising means for executing a rounding process with respect to the rate of change, wherein the forcible switching means switches the control mode based on a comparison of a value after the rounding process with the threshold value. 
   
   
     5. The diesel engine control device according to  claim 3 , wherein the rate of change is a rate of increase, two threshold values are provided on the increase side and the decrease side of the rate of increase, the forcible switching means starts the forcible switching when the rate of increase is equal to or greater than the increase side threshold value, and subsequently terminates the forcible switching when the rate of increase is equal to or less than the decrease side threshold value. 
   
   
     6. The diesel engine control device according to  claim 5 , wherein the increase side threshold value is set to a value lower than the decrease side threshold value. 
   
   
     7. The diesel engine control device according to  claim 1 , comprising an EGR device for recirculating a part of exhaust gas to the gas inlet side, and EGR control means for executing control so that the actual EGR ratio approaches the target EGR ratio as a target value, wherein the target EGR ratio of the premixed injection mode of the premixed region is set to 50% or greater. 
   
   
     8. The diesel engine control device according to  claim 1 , wherein when the control mode is switched, at least one of the normal switching means and the forcible switching means gradually changes the target values of one control mode into the target values of the other control mode. 
   
   
     9. The diesel engine control device according to  claim 1 , wherein when the control mode is switched, at least one of the normal switching means and the forcible switching means starts to change the target values of a fuel system behind the change in the target values of a gas inlet system. 
   
   
     10. The diesel engine control device according to  claim 1 , wherein, in the normal injection mode, a small quantity pilot injection and a large quantity main injection are carried out, and, in the premixed injection mode, only a main injection is carried out;
 the target values comprise at least the target pilot injection quantity, the target pilot injection timing, the target main injection quantity, and the target main injection timing in the normal injection mode, as well as the target main injection quantity and the target main injection timing in the premixed injection mode; 
 the target pilot injection quantity and the target pilot injection timing in the normal injection mode are associated with the target main injection quantity and the target main injection timing in the premixed injection mode respectively; and 
 when switching control modes, at least one of the normal switching means and the forcible switching means effects changes between the target pilot injection quantity in the normal injection mode and the target main injection quantity in the premixed injection mode, and effect changes between the target pilot injection timing in the normal injection mode and the target main injection timing in the premixed injection mode. 
 
   
   
     11. The diesel engine control device according to  claim 1 , wherein the engine comprises a reentrant type cavity provided in the top of a piston, and an injector whose injection angle is set so that the injected fuel enters the cavity in any of the control modes. 
   
   
     12. A diesel engine control device that controls the injection quantity and injection timing of fuel injected into a cylinder of a diesel engine,
 wherein are provided two control modes of: a normal injection mode in which the injection quantity and injection timing are controlled so that the injected fuel ignites near compression top dead center during an injection period; and a premixed injection mode in which the injection quantity and injection timing are controlled so that fuel injection is completed before compression top dead center and the injected fuel ignites near compression top dead center after a premixing period, 
 an entire engine operating region is divided into at least two regions, which are a normal region and a premixed region, 
 the diesel engine control device comprising: normal switching means for switching the control mode so that the normal injection mode is implemented when the actual engine operating conditions are in the normal region, and the premixed injection mode is implemented when the actual engine operating conditions are in the premixed region; and 
 forcible switching means for forcibly switching one control mode to the other control mode when the engine enters a predetermined transition state while, in the one engine operating region, the one corresponding control mode is being implemented; 
 wherein the forcible switching means switches the control mode based on a comparison of a rate of change of an engine load with a predetermined threshold value. 
 
   
   
     13. The diesel engine control device according to  claim 12 , further comprising means for executing a rounding process with respect to the rate of change, wherein the forcible switching means switches the control mode based on a comparison of a value after the rounding process with the threshold value. 
   
   
     14. The diesel engine control device according to  claim 12 , wherein the rate of change is a rate of increase, two threshold values are provided on the increase side and the decrease side of the rate of increase, the forcible switching means starts the forcible switching when the rate of increase is equal to or greater than the increase side threshold value, and subsequently terminates the forcible switching when the rate of increase is equal to or less than the decrease side threshold value. 
   
   
     15. The diesel engine control device according to  claim 14 , wherein the increase side threshold value is set to a value lower than the decrease side threshold value.